US 20060032479 A1
A system and method for controlling operation of cylinder with at least an intake and exhaust valve and a piston are described. In one aspect, the method comprises maintaining at least one of the intake and exhaust valves in a closed position during a period. Further, closing the other of the intake and exhaust valves with the piston at a first position from, and then opening the other of the intake and exhaust valves at a second position of the piston closer to bottom center than said first position, during said period.
1. A method for controlling operation of cylinder with at least an intake and exhaust valve and a piston, the engine in a vehicle, the method comprising:
in response to a tip out, maintaining at least one of the intake and exhaust valves in a closed position during a period, and closing the other of the intake and exhaust valves with the piston at a first position from, and then opening the other of the intake and exhaust valves at a second position of the piston closer to bottom center than said first position, during said period.
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12. A computer readable storage medium having instructions therein for controlling operation of cylinder with at least an intake and exhaust valve and a piston, the engine in a vehicle, the medium comprising:
instructions for, in response to a driver tip out, maintaining at least one of the intake and exhaust valves in a closed position during a period, and operating the other of the intake and exhaust valves in open position, then closing the other of the intake and exhaust valves from said open position with the piston at a first position, and then opening the other of the intake and exhaust valves at a second position of the piston closer to bottom center than said first position, during said period.
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17. A system for a cylinder of an engine of a passenger vehicle on the road, comprising:
a cylinder with at least an intake and exhaust valve and a piston;
a camshaft adapted to actuate said exhaust valve of said cylinder;
an electromechanical actuator adapted to actuate said intake valve of said cylinder;
a plastic intake manifold coupled to said cylinder; and
a controller for, in response to a driver tip out, and during a period with said exhaust valve substantially closed: operating with the intake valve open, then closing the intake valve with the piston at a first position, and then opening the intake valve at a second position of the piston closer to bottom center than said first position.
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The present description relates generally to systems for controlling engine braking during deceleration and/or traction control in an internal combustion engine of a passenger vehicle traveling on the road, and more particularly to controlling opening and/or closing timing of electromechanical intake and/or exhaust valves in the engine.
Internal combustion engines generally produce engine output torque by performing combustion in the engine cylinders. Specifically, each cylinder of the engine inducts air and fuel and combusts the air-fuel mixture, thereby increasing pressure in the cylinder to generate torque to rotate the engine crankshaft via the pistons. One method to improve engine fuel economy during deceleration is to deactivate fuel injection to all or a selected group of cylinders to thereby reduce combustion torque and increase engine braking.
The above approach can provide engine braking from engine friction and pumping work (due to manifold vacuum). The compression and expansion of air in the cylinders during the compression and expansion stroke results in energy storage and recovery, and thus may not contribute to engine braking. As such, one approach to increase engine braking is referred to as a “Jake Brake”. A Jake Brake opens the exhaust valve at top dead center of compression, thereby reducing or eliminating the energy recovery of the expansion stroke. This, in turn, can increase engine braking significantly since the unrestrained expansion is dissipating energy stored during the compression stroke. An example application is described in U.S. Pat. No. 6,192,857.
However, the inventors herein have recognized several issues with such a system. For example, since the Jake Brake uses compression work to generate braking torque, it must dissipate the stored energy of compression by allowing unrestrained expansion of the compressed gasses. This release of compressed gasses may cause high noise emissions due the rapid release of compressed gas. Furthermore, the maximum amount of pressure generated by compression may be limited due to opening force requirement of the exhaust valve, thereby potentially limiting braking torque available.
In one approach, a method for controlling operation of cylinder with at least an intake and exhaust valve and a piston, the engine in a vehicle, may be used. The method comprises:
maintaining at least one of the intake and exhaust valves in a closed position during a period, and closing the other of the intake and exhaust valves with the piston at a first position from, and then opening the other of the intake and exhaust valves at a second position of the piston closer to bottom center than said first position, during said period.
In this way, it may be possible to reduce flow passing from the intake to the exhaust, while also improving engine braking compared with compression braking systems and reducing noise. In other words, by operating as noted above, it may be possible to generate expansion work braking in the cylinder, in which gasses are expanded in the cylinder and then gasses from a manifold are allowed to expand into the cylinder to dissipate the stored energy. In this way, lower pressure differentials can be achieved compared with compression braking, which may also reduce noise generation.
Note that the above approach can be used alone, or combined with compression braking, if desired. Also note that the opening of the intake valve can be either full or partial opening. Further note that the period can be an expressly defined period, or a variable period, for example.
Implementation of fuel-cut operation on engines, such as deceleration fuel shut-off (DFSO), may be challenging due issues such as:
In other words, net flow through the engine may transport heat from the catalyst into the surrounding environment, which may degrade catalyst efficiency. Additionally, the engine braking characteristic may be altered if fuel-cut operation is used.
Electromechanical valve actuation (EVA) may be used with fuel-cut operation to improve performance. In other words, EVA valves on one side of the engine (intake/exhaust) may be deactivated in the closed position, which may prevent or reduce the breakthrough of air and unwanted oxygen storage. Further, the engine braking torque level can be controlled by opening and closing the valves on the other side of the engine at an appropriate time during the engine cycle to provide expansion or compression work. This may effectively provide a dashpot to smooth the transitions, while at the same time reduce catalyst cooling and oxygen saturation.
Note that as described in more detail below, several different schemes may be employed. In one example, the intake valve(s) may be deactivated and then the exhaust valve(s) can be opened and closed to obtain the desired average braking torque. In another example, the exhaust valve(s) can be closed and the intake valve(s) can be opened and closed. Further combinations of these approaches can be used, as well as operating some cylinders in an engine braking mode, and others combusting air or in a deactivated stated without compression or expansion braking. Also note that in different operating modes, different types of engine braking can be used. For example, in conditions which require increased braking levels, compression braking (or combined compression and expansion braking) can be used, whereas during conditions which require less engine braking, expansion braking can be used.
In some cases, the following advantages may be achieved:
Referring now to
Internal combustion engine 10 may comprise a plurality of cylinders, one cylinder of which, shown in
As described more fully below with regard to
Intake manifold 44 communicates with throttle body 64 via throttle plate 66. Throttle plate 66 is controlled by electric motor 67, which receives a signal from ETC driver 69. ETC driver 69 receives control signal (DC) from controller 12. In an alternative embodiment, no throttle is utilized and airflow is controlled solely using valves 52 and 54. Further, when throttle 66 is included, it can be used to reduce airflow if valves 52 or 54 become degraded, or to create vacuum to draw in recycled exhaust gas (EGR), or fuel vapors from a fuel vapor storage system having a valve controlling the amount of fuel vapors.
Intake manifold 44 is also shown having fuel injector 68 coupled thereto for delivering fuel in proportion to the pulse width of signal (fpw) from controller 12. Fuel is delivered to fuel injector 68 by a conventional fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown).
Engine 10 further includes conventional distributorless ignition system 88 to provide ignition spark to combustion chamber 30 via spark plug 92 in response to controller 12. In the embodiment described herein, controller 12 is a conventional microcomputer including: microprocessor unit 102, input/output ports 104, electronic memory chip 106, which is an electronically programmable memory in this particular example, random access memory 108, and a conventional data bus.
Controller 12 receives various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including: measurements of inducted mass air flow (MAF) from mass air flow sensor 110 coupled to throttle body 64; engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling jacket 114; a measurement of manifold pressure from MAP sensor 129, a measurement of throttle position (TP) from throttle position sensor 117 coupled to throttle plate 66; a measurement of transmission shaft torque, or engine shaft torque from torque sensor 121, a measurement of turbine speed (Wt) from turbine speed sensor 119, where turbine speed measures the speed of shaft 17, and a profile ignition pickup signal (PIP) from Hall effect sensor 118 coupled to crankshaft 13 indicating an engine speed (N). Alternatively, turbine speed may be determined from vehicle speed and gear ratio.
In an alternative embodiment, where an electronically controlled throttle is not used, an air bypass valve (not shown) can be installed to allow a controlled amount of air to bypass throttle plate 62. In this alternative embodiment, the air bypass valve (not shown) receives a control signal (not shown) from controller 12.
Also, in yet another alternative embodiment, intake valve 52 can be controlled via actuator 210, and exhaust valve 54 actuated by an overhead cam, or a pushrod activated cam. Further, the exhaust cam can have a hydraulic actuator to vary cam timing, known as variable cam timing.
In still another alternative embodiment, only some of the intake valves are electrically actuated, and other intake valves (and exhaust valves) are cam actuated.
Further, various types of valve control actuators can be used, in addition to the electromechanical mechanical approach listed above. For example, any type of valve control mechanism can be used, such as, for example, hydraulic variable cam timing actuators, cam switching actuators, electro-hydraulic actuators, or combinations thereof.
Note also that the above approach is not limited to a dual coil actuator, but rather it can be used with other types of actuators. For example, the actuators of FIGS. 4 or 6 can be single coil actuators. In any case, the approach synergistically utilizes the high number of actuators (engine valves, in this example) to aid in reducing the number of power devices and the size of the wiring harness. Thus, the dual coil actuator increases this synergy, but a single coil actuator would have similar potential.
Switch-type position sensors 228, 230, and 232 are provided and installed so that they switch when the armature 220 crosses the sensor location. It is anticipated that switch-type position sensors can be easily manufactured based on optical technology (e.g., LEDs and photo elements) and when combined with appropriate asynchronous circuitry they would yield a signal with the rising edge when the armature crosses the sensor location. It is furthermore anticipated that these sensors would result in cost reduction as compared to continuous position sensors, and would be reliable.
Controller 234 (which can be combined into controller 12, or act as a separate controller) is operatively connected to the position sensors 228, 230, and 232, and to the upper and lower coils 216, 218 in order to control actuation and landing of the valve 212.
The first position sensor 228 is located around the middle position between the coils 216, 218, the second sensor 230 is located close to the lower coil 218, and the third sensor 232 is located close to the upper coil 216.
As described above, engine 10, in one example, has an electromechanical valve actuation (EVA) with the potential to maximize torque over a broad range of engine speeds and substantially improve fuel efficiency. The increased fuel efficiency benefits are achieved by eliminating the throttle, and its associated pumping losses, (or operating with the throttle substantially open) and by controlling the engine operating mode and/or displacement, through the direct control of the valve timing, duration, and or lift, on an event-by-event basis.
In one example, controller 234 includes any of the example power converters described below.
While the above method can be used to control valve position, an alternative approach can be used that includes position sensor feedback for potentially more accurate control of valve position. This can be use to improve overall position control, as well as valve landing, to possibly reduce noise and vibration.
As illustrated above, the electromechanically actuated valves in the engine remain in the half open position when the actuators are de-energized. Therefore, prior to engine combustion operation, each valve goes through an initialization cycle. During the initialization period, the actuators are pulsed with current, in a prescribed manner, in order to establish the valves in the fully closed or fully open position. Following this initialization, the valves are sequentially actuated according to the desired valve timing (and firing order) by the pair of electromagnets, one for pulling the valve open (lower) and the other for pulling the valve closed (upper).
The magnetic properties of each electromagnet are such that only a single electromagnet (upper or lower) need be energized at any time. Since the upper electromagnets hold the valves closed for the majority of each engine cycle, they are operated for a much higher percentage of time than that of the lower electromagnets.
The following description describes various example processes and valve timings that may be used to generate and adjust engine braking torque.
One example is described in
By varying the valve opening time, the level of negative work changes, which then establishes the engine braking torque characteristic.
Note that in some cases, a limit may be imposed on compression pressure obtained for valve opening timing. For example, the latest practical valve opening (vo) time can occur when the pressure in the cylinder is about 10 bar. Pressures higher than a limit (if applicable) may make it more difficult to open the valve. A limit check may be placed on any desired valve opening timing that may occur higher than a threshold pressure, if desired.
Also note that while
In the example of generating braking torque via compression braking, the valve(s) on one side of the engine may be maintained closed, and the valve(s) on the other side of the engine can be closed from an open position at a first piston position, and then opened at a second piston position closer to the top center piston position than the first position. Note that this can be done within a single upward piston stroke, or over one or more cycles (e.g., valve(s) on both sides of the engine are closed for one or more strokes in between the closing at the first position and opening at the second position).
As noted above, in the approach illustrated by the example of
When this is performed on the intake side (via actuation of one or more intake valves while exhaust valves are closed), noise may be reduced by closing a throttle plate in the intake manifold. Such operating may reduce the ability for noise to travel through the induction system and increase noise suppression. Further, in the case where this is performed on the exhaust side (via actuation of one or more exhaust valves while the intake valve(s) is maintained closed), noise may be reduced compared with a Jake brake since there is reduce net flow out of the engine. Further, by varying the opening/closing timing of the exhaust valve during this mode of operation, noise may also be reduced.
Another example is illustrated in
In the example of generating braking torque via expansion braking, the valve(s) on one side of the engine may be maintained closed, and the valve(s) on the other side of the engine can be closed from an open position at a first piston position, and then opened at a second piston position closer to the bottom center position than the first position. Note that this can be done within a single downward piston stroke, or over one or more cycles (e.g., valve(s) on both sides of the engine are closed for one or more strokes in between the closing at the first position and opening at the second position).
One result obtained with expansion work is that different pressure differentials relative to atmospheric pressure can be obtained compared with compression braking, which can be explained from the relationship of the gasses defined for a polytropic process of an ideal gas (pVγ=constant, where γ is the specific heat ratio). In other words, expanding the clearance volume gasses (filled at atmospheric) with a given compression ratio of can yield a pressure differential less than compressing the maximum volume (clearance volume plus displacement filled at atmospheric pressure). As one example, the maximum pressure (Pmax) that can be achieved in the cylinder is roughly 21 bar (where atmospheric is roughly 1 bar) with a compression ratio of 10 and γ of 1.33, which gives roughly a 20 bar pressure differential. Alternatively, the minimum pressure that can be obtained is a complete vacuum (0 bar), which gives a maximum pressure differential of roughly 1 bar for expansion braking. Freely expanding the compressed gas in compression braking may thus generate more noise in the engine than compared with expansion braking, especially in the case of a plastic intake manifold if intake side expansion/compression work is used. The above is one example theory that may explain operation, and is not relied upon herein.
Note that in the case of creating engine brake torque in the cylinder, gasses may also be moved into and out of the cylinder via the same side (intake/exhaust of the engine), and thus may reduce flow through the exhaust (at least from that cylinder). Further, in the case of expansion work, engine noise may be reduce (on either the intake or exhaust side) since gasses are not being forced out of the cylinder at high pressure, but rather are being forced into the cylinder. Noise may be further reduced on the intake side as well via a closed, or partially closed, throttle plate.
Note also that in the case of expansion work, there may not be a pressure limit on valve opening since the valve opening may actually be assisted by the vacuum created in the cylinder.
In still another alternative embodiment, it may be possible to combine both expansion and compression work.
As noted above for either the compression or expansion braking example, various modifications can be made to valve opening/closing timing to vary the braking torque created. Further, the gasses may be moved into and out of the cylinder on either the intake or exhaust side.
Also, for any of the above approaches, only some of the cylinders may be operated to generate engine braking, while other cylinders are operated with all valves closed, or combusting and air-fuel mixture. Also, different cylinders can carry out different modes of engine braking.
Note that the implementation of expansion and/or compression braking may generate more engine brake torque than approaches that rely on engine pumping work (although this may be combined with the present approach, if desired). In such engine, the theoretical lower limit for net mean effective pressure NMEP while using fuel-cut would be on the order of −1 bar. This is in contrast to the scheme shown in
Note also that the above compression and/or expansion braking processes may occur in less than two strokes of a piston for that cylinder. As such, it may be possible to perform two braking cycles over a four-stroke cycle. Alternatively, only one braking cycle can be performed of four (or more) strokes, thereby spreading the torque over a greater crank angle and resulting in lower net engine braking.
Various examples illustrating at least some of the alternative embodiments, as well as other alternative embodiments, are shown in
In each example, a valve on one side of the engine (e.g., intake side, exhaust side) is maintained closed for a period, and during that period, a valve on the other side of the engine is moved from a closed position, to an open position (which may be fully opened, partially opened, etc.), and back to a closed position. The period can be fixed or variable. Further, the period can be a time period, a period defined by a number of rotation degrees of the engine, or left undefined to be determined by operating conditions or feedback from a sensor.
As indicated above, it may be possible to double the expansion work for a given valve timing by adding an additional expansion work cycle indicated by the dashed line. Alternatively, the expansion cycle can be performed every 3 stroke, every 5 stroke, or less often such as every 6, 7, or 8 strokes. Also, the example of
As stated above, in each of the figures, an intake valve is indicated at (I) and an exhaust valve at (E). Note however, that more than one intake or more than one exhaust valve may be used. In such a case, all of the intake or all of the exhaust valves may follow the timings indicated. Alternatively, in the case where there are 4 valves per cylinder (2 intakes and 2 exhausts), one group of valves may follow the timings indicated, while only one of the valves in the other group follows the timing indicated. For example, in any of the examples illustrated in
Specifically, in one example, compression braking is used, although expansion braking may be used as illustrated by the dotted lines. Further, as noted in a previous example, the braking torque can be increased by performing a compression/expansion cycle on every available stroke, or by using a combination of expansion and compression braking (although these are not shown in
Note that in any of the Figures herein, the valves may not move instantaneously as shown, as such the Figures show valve motion for illustrative purposes. Rather, valve opening and valve closing may take a variable amount of time or degrees.
Note that in some example embodiments, an electronically controlled throttle plate can be used in the engine. The throttle can be adjusted based on operating conditions to generate vacuum, if desired. Also, during expansion or compression braking on the intake side of the engine, the throttle plate can be closed, or partially closed, to reduce noise from passing out through the induction system.
Referring now to
As will be appreciated by one of ordinary skill in the art, the specific routines described below in the flowcharts may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the disclosure, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. Further, these Figures graphically represent code to be programmed into the computer readable storage medium in controller 12.
Referring specifically to
Next, in step 912, the routine determines desired net engine output (e.g., torque) from the driver's request. Further, additional parameters may be taking into account, such as traction control, cruise control, vehicle or engine operating conditions, degradation conditions, or combinations thereof.
In step 914, the routine determines whether the desired engine output, is less than a first limit. In this example, the routine determines whether the desired engine output torque is less than a first threshold TQ1, which may be zero, or a small or negative torque. Alternatively, it may be the output torque provided by deactivating all cylinder valves (e.g., friction torque). Still further, TQ1 may be a minimum possible torque available by combusting all cylinders at a minimum airflow.
When the answer to step 914 is NO, the routine continues to step 916 where combustion may be performed in all cylinders. Further, in this mode, engine output is controlled by varying the intake and/or exhaust valve timing, for example. From step 916, the routine continues to the end.
Alternatively, when the answer to step 914 is YES, the routine continues to step 918, where a determination is made as to whether the desired engine output, is less than a second limit. In this example, the routine determines whether the desired engine output torque is less than a second threshold TQ2, which may be less than TQ1. When the answer to step 918 is NO, the routine continues to step 920 where combustion may be performed in a reduce number of cylinders. Specifically, in step 920, the routine determines a number of cylinders in which to carry out combustion, and a number in which to deactivate valves, to provide the desired torque. Further, in this mode, engine output is controlled by varying the intake and/or exhaust valve timing of operating cylinders, for example. Further, negative torque may be controlled by controlling valve timings for deactivated cylinders, as described herein.
Alternatively, when the answer to step 918 is YES, the routine continues to step 922 where the routine determines a number of cylinders to provide engine braking torque. In one embodiment, the routine also determines the number of strokes between engine braking provided by compression or expansion work in a cylinder. In this way, it may be possible to vary not only valve timing to vary the braking torque achieved, but also vary the number of expansion and/or compression events in a given number of engine cycles to vary the cycle averaged engine braking torque.
Next, in step 924, the routine selects whether expansion braking, compression braking, or both, are selected for any of the cylinders selected to provide engine braking action via expansion or compression work. Note that each cylinder can be operated with a common approach, or different cylinders can provide different types of braking, if desired. Then, in step 926, the routine selects whether intake and/or exhaust valve actuation may be used to provide expansion or compression work in the selected cylinders. Again note that each cylinder can be operated with a common approach, or different cylinders can provide intake and/or exhaust side braking, if desired.
Then, in step 926, the routine continues to step to deactivate fuel, spark and the selected valves to provide the desired engine braking mode(s). Finally, in step 928, the routine adjusts the opening and/or closing timing of the active valves on the selected cylinder to vary the respective braking torque of the cylinders to desired values. Then, the routine ends.
This illustrates one example approach for smoothly and continuously controlling the braking torque, which may allow improved engine braking and vehicle control.
Thus, while this routine illustrates one embodiment, various others can be used. For example, a routine can be used which controls vehicle acceleration or deceleration rate of the vehicle using the measured vehicle speed. Alternatively, a routine can be used in which a desired deceleration rate is based on vehicle speed, and then the engine braking is adjusted to maintain or achieve the desired deceleration rate. Further, valve timings can be adjusted to provide more braking at higher speeds, and more braking at higher acceleration rates.
In one example, engine braking torque may be controlled by controlling the intake and/or exhaust valve timing to deliver a desired level of compression, expansion, or both. In the following example embodiment, exhaust valve opening timings for the compression, expansion, and combined mode are developed. However, these same techniques could be used to develop closing timing, intake valve (opening/closing) timings, or combinations thereof.
Note that, as described above, different engine braking techniques can be used in different situations. For example, in conditions where high engine braking is used, a portion or all of the engine cylinders can be operated with intake and/or exhaust side compression (optionally in combination with expansion) braking to generate desired high levels of engine braking. Alternatively, in conditions in which low engine braking is used, only expansion (intake or exhaust side) braking (in some or all of the cylinders) can be used to reduce noise while still providing desired braking. In this way, improved overall performance may be achieved. Also, as noted, in different operating modes, different numbers and selected cylinders may be operated in an engine braking mode, while other cylinders are operated with all intake/exhaust valves closed without carrying out combustion (i.e., without expansion/compression braking). In this way, greater brake torque resolution may be achieved. While desired torque is one operating condition that may be used in selected between any or all of the above braking modes and combinations, other parameters may be used, such as engine speed, vehicle speed, vehicle acceleration, driver pedal position, engine airflow, or combinations thereof. Thus, the following are example modes that may be use:
Also, on one embodiment, a characterization of the exhaust valve timing vs. average torque per cylinder may be used. Simulation results of the EVA engine under exhaust valve compression and expansion torque control are presented. These results are used to further develop a map between the exhaust valve opening timing, EVO, and the resulting braking torque by adjusting the average torque per cylinder models. Finally an EVO vs. average compression or expansion torque map development procedure is presented.
In one example, the compression braking work described above can be achieved by setting the exhaust valve closing timing, EVC, to close the exhaust valves near BDC, to maximize the trapped air volume, and by controlling the exhaust valve opening timing, EVO, to control the compression pressure and the resulting negative torque per cylinder. Also, as noted above, this exhaust valve timing method can be used in a 2-stroke mode (i.e., two compression cycles over a four stroke cycle) to further increase the compression torque per cylinder for a given maximum valve opening, blow-off, pressure or in a 4-stroke mode (e.g., one compression cycle over a four stroke cycle), or more. For example, a 4-stroke mode it can be used in cases where the 4-stroke mode provides improved low torque resolution or when the minimum valve open duration prevents the use of the 2-stroke mode, e.g. at high engine speeds.
The expansion braking work, on the other hand, can be achieved by setting the exhaust valve closing timing, EVC, to close the exhaust valves near TDC, to minimize the trapped air volume, and by controlling the exhaust valve opening timing, EVO, to control the expansion pressure and the resulting negative torque per cylinder. This exhaust valve timing method can also be used in 2-stroke mode to increase the expansion torque per cylinder for a given EVO timing, or in 4 (or more) -stroke mode. For example a 4-stroke mode can b used in cases where the 4-stroke mode provides improved low torque resolution or when the minimum valve open duration prevents the use of the 2-stroke mode, e.g. at high engine speeds.
The mixed compression/expansion mode can be implemented by combining the valve timing from compression work when the piston is moving up with the valve timing of expansion work when the piston is moving down. Also, as noted in
Also, in still another example, a cylinder can alternatively (every cycle, or every few cycles) switch between compression and expansion braking to reduce potential oil migration into the cylinder.
Next, a method to convert desired average compression/expansion torque to a desired EVA exhaust valve timing is developed. Note that this is just one example approach, and other approaches could be used, such as basing the map on engine testing data. To produce a desired engine or vehicle response by controlling the exhaust valve timing as described above for this embodiment, either feedback or feed-forward techniques may be used, for example. If feedback is used then EVO and EVC are controlled as a function of an error state, such as the error in demanded torque, vehicle or wheel or engine deceleration or velocity. If feed-forward is used (either alone or in addition to feedback control) then EVO and EVC are at least partially controlled in an open loop manner using a mapping between compression and/or expansion torque and EVO, EVC and an engine operating point. The following examples show the development of a feed-forward technique for scheduling EVO as a function of desired compression or expansion torque.
The relationship between average compression /expansion torque per cylinder vs. EVO can be developed by starting with the ideal gas pressure equation for an open thermodynamic system, Eqs. (1), and eliminating the terms that may not apply while the valves are closed.
As the valves are closed, the mass flow rate terms can be assumed to be nearly zero. Further there is no combustion, which gives, Eq. (2).
Where qw is the heat transfer between the gas in the cylinder and the piston and cylinder walls, P is pressure, V is the cylinder volume, and γvol is the polytropic constant. If the heat transfer is neglected, Eq. (2) can be reduced to the closed volume adiabatic expansion equation:
Using Eq (3) and the torque per cylinder due to cylinder pressure, a known expression for the average torque per cylinder, over a 360 degree cycle can be derived.
Where Apist is the piston area, θ1 is π for compression and zero for expansion, θ2 is 3π for compression and 2π for expansion, and V is the piston volume, which is given by:
where V0 is the cylinder clearance volume, LJ s the crankshaft center to connecting journal pin center length and Lcr is the connecting rod length and θ is the crankshaft angle for the individual cylinder. By equating the crankshaft angle θ to the valve timing angle for each cylinder, combining Eqs. (3) through (6) and assuming that the cylinder pressure, P, at EVC is equal to the exhaust manifold pressure, it is possible to calculate the relationship between average compression and/or expansion torque and EVO over the 360 degree period between θ1 and θ2. Further the period before or after θ1 to θ2 in 4 stroke mode, when the exhaust valve is open, can be accounted for by noting that Equ. (4) is equal to zero if the cylinder pressure is constant.
Setting θ1 equal to π, θ2 equal to 3π, P equal to Pexh when the valve is open, and a maximum blow-off pressure of 7 Bar for the EVA engine,
Using tables of EVO vs. Tcyl for both compression and expansion torque, derived from
A pressure blow down model may be developed using a cosine function to approximate the pressure drop from the pressure at EVO to the exhaust pressure over a duration, θDur, which can either be fixed or a function of engine speed and other engine operating parameters. The blow down pressure model is given by:
A pressure rise model for the expansion cycle may be developed using a cosine function to approximate the pressure rise from the pressure at EVO to the exhaust pressure over a duration, θDur, which can either be fixed or a function of engine speed and other engine operating parameters. The pressure rise model is given by:
The expansion Tcyl vs. EVO curve in
By using the average per cylinder compression and\or expansion torque given by Eqs. (3) through (6) and the pressure blow-off and rise models given by Eqs. (7) and (8), a map or regression of EVO as a function of Tcyl, EVC and engine operating conditions (see
In this example, by combining a mapping based upon Eqs. (3)-(8), as two or multi-dimensional tables and\or regressions, with adjustments to the base map as a function of engine speed or operating points, for example, maps of compression and\or expansion EVO vs. Tcyl can be developed for use in the EVA engine control strategy. An example process flow-chart for the development of compression and\or expansion EVO vs. Tcyl maps is shown in
Referring now to
Referring now to
Therefore, in a system with at least some electrically actuated engine valves, improved results may be obtained by combining torque production of firing and non-firing engine cylinders, in one embodiment. In other words, while a throttle may still be used to control torque, if desired, the maximum engine braking torque that can be generated with a throttle may be limited by the maximum vacuum that can be generated in the intake, e.g., less than 1 Bar. However, with electronic valve control (alone or in combination with a throttle) may generate higher levels of braking torque if required, as described above.
Therefore, in one embodiment, a controller first determines a number and the configuration of firing/non-firing cylinders, such as the various examples described above. Then, the controller determines a desired mode for the non-firing cylinders (e.g., expansion braking, compression braking, combinations of expansion/compression braking, intake side, exhaust side, or combinations thereof). Mode selection criteria may include available torque range, NVH, desired torque, vehicle and engine conditions, fuel economy, and/or combinations thereof.
Next, the controller sets valve timing on the firing cylinders (if any) to generate positive torque, and sets valve timing on the non-firing cylinders (if any) to generate negative torque.
Thus, the controller varies valve timing on the active cylinders to generate positive torque, varies valve timing on the inactive cylinders to generate negative torque (intake/exhaust expansion/compression braking), and may use torque control to determine the active/inactive cylinder valve timing that will produce the desired engine torque with the best fuel economy and NVH in response to a commanded torque request.
An example potential positive indicated torque available from a range of active cylinder modes, on an 8 cylinder engine, is illustrated in
Referring now to
It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above converter technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. Also, approach described above is not specifically limited to a dual coil valve actuator. Rather, it could be applied to other forms of actuators, including ones that have only a single coil per valve actuator, and/or other variable valve timing systems, such as, for example, cam phasing, cam profile switching, variable rocker ratio, etc.
The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.